Film made from ethylene-higher olefin copolymers, known as linear low density polyethylene, has toughness properties superior to film made from conventional low density polyethylene prepared under high pressure conditions. However, linear low density polyethylene has a low melt strength so that it is difficult to process at high speed and maintain a stable bubble in the blown tubular film process. The disadvantage of lower melt strength is also apparent in the blow molding of linear low density polyethylene and high density polyethylene. In accordance with this invention melt strength of polyethylenes can be improved without substantially affecting their desirable properties.